We find the district court’s concern with “what the invention is” misplaced, and its requirement that the ‘081 drawings “describe what is novel or important” legal error. There is “no legally recognizable or protected `essential’ element, `gist’ or `heart’ of the invention in a combination patent.” Aro Mfg. Co. v. Convertible Top Replacement Co., 365 U.S. 336, 345, 81 S.Ct. 599, 604, 5 L.Ed.2d 592 (1961). “The invention” is defined by the claims on appeal. The instant claims do not recite only a pair of semi-circular lumens, or a conical tip, or a ratio at which the tip tapers, or the shape, size, and placement of the inlets and outlets; they claim a double lumen catheter having a combination of those features. That combination invention is what the ‘081 drawings show. As the district court itself recognized, “what Mahurkar eventually patented is exactly what the pictures in serial ‘081 show.” 745 F.Supp. at 523, 17 USPQ2d at 1357.
Vas-Cath Inc. v. Mahurkar, 935 F.2d 1555, 1565 (Fed.Cir.1991).